It is often desired to control the flow rate of fluid flowing through assay devices. For example, lateral flow strips typically employ a membrane through which a test sample flows before reaching a detection zone. Most conventional lateral flow strips are designed for test samples that are readily available in large quantities (e.g., urine). However, when the test sample is blood, the collection of a large sample may cause undue pain to the patient. Thus, one technique that has been utilized is to “spot” the sample directly only the membrane surface. Thereafter, a diluent is used to wash away the test sample and carry it to the detection zone. Unfortunately, variations associated with sample transfer and diffusion of the sample to the membrane result in a flow that is largely uncontrolled and uneven before reaching the detection zone. This may have an adverse affect on the accuracy of the device because the amount of analyte captured across the detection zone is not consistent at the time of measurement.
As such, a need currently exists for a simple and efficient technique for controlling the flow rate of a fluid through a membrane of an assay device.